非晶合金薄膜在复杂应力条件下的微观形变机理和破坏准则

The lack of plastic deformation of bulk amorphous alloys under tensile load restricts their wide applications in aerospace, defense, energy and other fields. Resolving this issue requires further studies on the plastic deformation mechanisms of amorphous alloys at the micro- and nano-scale. In this project, we propose a new sample preparation for synthesizing amorphous alloy thin films, which could avoid the potential contamination using the traditional preparation protocol. We also plan to build a novel bulge-test setup based on the digital holographic microscopy technology, which will be able to perform accurate mechanical measurements on amorphous alloy thin films to characterize their key mechanical properties such as elastic modulus, yield strength, plastic deformation, and stress relaxation behavior. The experimental results produced by the novel experimental setup, together with molecular dynamic simulation results and theoretical analysis, will help explaining the size effects on the plastic deformation mechanisms of amorphous alloys; revealing the microscopic mechanism of the brittle-to-ductile failure mode transition; and establishing the failure criterion for amorphous alloy thin films with varying thicknesses under complex stress states. The research of this project will provide insight into fundamental scientific problems, such as the verification of microstructural origins of the deformation mechanisms in amorphous alloys; and provide useful guidance for developing new methods to improve the ductility of bulk amorphous alloys.

宏观块体非晶合金在拉伸载荷下缺乏塑性变形制约了其在航空航天、国防、能源等领域的广泛应用。要突破这一瓶颈需要对非晶合金的微观塑性变形机理进行深入的研究。本项目提出全新设计的微纳米尺度非晶合金薄膜样品制备方案避免对样品的污染；计划设计和搭建基于数字全息显微镜技术的鼓膜力学实验平台，对微纳尺度非晶合金薄膜在复杂应力加载条件下的弹性模量，屈服强度，塑性变形，应力弛豫行为等关键力学性质进行精确的实验表征。通过全新的实验表征方法，结合分子动力学模拟以及理论分析，研究样品尺寸对非晶合金塑性变形机理的影响；揭示非晶合金脆韧断裂转换的微观机理；建立非晶合金薄膜在样品尺寸以及复杂应力条件因素影响下的破坏准则。本项目的研究将为验证非晶金属变形机制的微观结构起源等关键科学问题，以及探索改进非晶合金宏观拉伸塑性的方法等工程问题提供指导。

非晶合金由于内部不存在晶体金属中的位错、晶界等缺陷，具备高强度、高硬度、高弹性极限等优异性能，在国防、航空航天等领域具有广阔的应用前景。但同时，非晶合金也不具备晶体材料所具有的塑性变形机制，在常温时缺乏宏观拉伸塑性，这严重制约了非晶合金的工程应用。本项目针对非晶合金在微纳米尺度下的率相关剪切失稳机理及黏弹塑性力学行为微观机制开展了研究。本项目首先构建了热力学自洽的非晶黏弹塑性本构模型，建立起微观原子流动与宏观塑性变形之间的关联。其次，发展了新的样品制备技术，制备出高质量、一致性好的非晶合金纳米薄膜样品。基于原子力显微镜平台，实现了非晶合金纳米薄膜样品的悬空压入加载，并发现纳米薄膜独特的疲劳行为。并且，本项目利用高功率激光脉冲实现了非晶合金箔材的超高应变率（107s-1以上）加载，测量得到非晶合金的拉伸强度趋近于材料的理想强度。本项目进一步探究了界面几何形状对非均质材料阻尼特性的影响，并发展了新型多尺度断裂力学框架，这对于理解非均质材料的变形机理具有重要意义。本项目的研究揭示了非晶合金剪切失稳的微观结构演化机制，对推动非晶合金及其它非均质材料体系在工程中的应用具有重要的理论指导意义。本项目共发表高水平SCI论文21篇，培养博士生3名，硕士生2名。